At present, the requirement of the development of the mobile communication is to be able to support a higher transmission rate, a better signal coverage and a higher resource utilization rate. The Relay technology can increase the coverage, and balance and increase the throughput of the cell, and the Relay Node (abbreviated as RN), compared with the base station, has a relatively smaller allocation cost, so the relay is considered as a critical technology in an evolution system of the 3rd Generation Partnership Project (abbreviated as 3GPP) Long Term Evolution (abbreviated as LTE, usually referring to Release 8 or Release 9 protocol edition, abbreviated as Rel-8 or Rel-9)—LTE-Advanced (abbreviated as LTE-A, usually referring to Release 10 protocol edition, abbreviated as Rel-10).
The LTE/LTE-A system downlink is based on the Orthogonal Frequency Division Multiplexing (OFDM) technology. In the OFDM system, the communication resources are in the time-frequency two-dimension form.
In the LTE/LTE-A system, the communication resources in the downlink are divided using the frame as a unit in the time direction. As shown in FIG. 1, a length of every radio frame is of 10 ms, including 10 sub-frames with the length of 1 ms. As shown in FIG. 2, every sub-frame is divided into two slots in the time direction as well. According to the difference of the lengths of the Cyclic Prefix (abbreviated as CP), every sub-frame can include 14 or 12 OFDM symbols. When the sub-frame adopts a Normal CP length, the sub-frame includes 14 OFDM symbols, and every slot contains 7 symbols; when the sub-frame adopts an Extended CP length, the sub-frame includes 12 OFDM symbols, and every slot contains 6 symbols.
In the LTE/LTE-A system, the communication resources in the downlink are in the frequency direction, and the resources are divided using the sub-carrier as a unit. Specifically, in the communication, the minimum unit of the allocated resources is Resource Block (RB), which corresponds to a physical resource block (PRB) of the physical resource. As shown in FIG. 2, one PRB includes 12 sub-carriers in the frequency domain, corresponding to a slot in the time domain. The two RBs in the sub-frame which are adjacent in the time domains are called a RB pair. The resource corresponding to one sub-carrier on every OFDM symbol is called the Resource Element (abbreviated as RE).
As shown in FIG. 2, a physical resource structure is provided with the normal CP length. If it is not especially illustrated hereinafter, the serial number of the OFDM symbol in the sub-frame is 0-13 when the normal CP length is adopted, and the OFDM symbol in the slot is numbered as 0-6; the serial number of the OFDM symbol in the sub-frame is 0-11 when the extended CP length is adopted, and the OFDM symbol in the slot is numbered as 0-5.
After introducing the relay station, it is equivalent to add one hop for the data transmission. Taking a two-hop system as an example, a communication mode of an original base station—a UE has been turned into a communication mode of a base station—a relay station—a UE, wherein, a base station—relay station link is called a relay link (a backhaul link or called a Un interface), a relay station—UE link is called an access link (or called a Uu interface), and a base station—UE link is called a direct link. In a multi-hop system, some UEs access the relay station, and finish the communication service through the relay station.
After introducing the relay station, the backward compatibility with the UE needs to be guaranteed, that is, it is guaranteed that the UE of the previous edition (such as LTE Release-8, abbreviated as Rel-8) also can access the relay station of the LTE-A system. At this time, it needs to, on condition of not influencing the communication of the subordinate UE of the relay station, set apart some resources to ensure the communication between the base station and the relay station. Now in the LTE-A system, it is determined that the base station—relay station communication and the relay station—UE communication are performed in the time division mode. Specifically, a part of the downlink sub-frames are set apart used for the base station—relay station communication, and these sub-frames are called Relay sub-frame (or called Un sub-frame). For the Rel-8 UE which is subordinate to the relay station, the relay sub-frame is indicated as the Multicast Broadcast Single Frequency Network (abbreviated as MBSFN) sub-frame, and the Rel-8 UE can skip these sub-frames, thus guarantying the backward compatibility with the Rel-8 UE when completing the base station—relay station communication. In the LTE-A system, the structure of the relay sub-frame is shown in FIG. 3.
The Relay Node sends the control information to the subordinate UE in the first 1 or 2 OFDM symbols of the relay sub-frame, and then after a transfer time interval switching from the sending state to the accepting state, it receives the downlink data information of the relay link from the base station. Because the relay station does not receive the Physical Downlink Control Channel (abbreviated as PDCCH), then one physical signal channel R-PDCCH (Relay-PDCCH, relay link PDCCH) needs to be redefined in the relay link used for the transmission of the downlink control information of the relay link.
Now in the discussion of the 3GPP LTE-A related technology, the discussion about the details of the R-PDCCH, such as, the resource element group (REG), etc., has not been fully developed yet. Therefore, how to determine to generate an effective REG of the relay link physical downlink control channel (R-PDCCH) becomes a technical problem which needs to be solved.